Continuous-type ink jet printing systems create printed matter by selective charging, deflecting and catching drops produced by one or more rows of continuously flowing ink jets. The jets themselves are produced by forcing ink under pressure through an array of orifices in an orifice plate. The jets are stimulated to break up into a stream of uniformly sized and regularly spaced droplets.
The approach for printing with these droplet streams is to use a charge plate to selectively charge certain drops, and to then deflect the charged drops from their normal trajectories. The charge plate has a series of charging electrodes located equidistantly along one or more straight lines. Electrical leads are connected to each such charge electrode, and the electrical leads in turn are activated selectively by an appropriate data processing system.
U.S. Pat. No. 4,636,808, which issued to Herron, describes a simple arrangement of the drop generator and the charge plate. U.S. Pat. No. 6,660,614 discloses anodic bonding, while U.S. Pat. No. 4,560,991 discloses a method of forming charge plates using electroforming. Both of these techniques are used in the practice of the preferred embodiment of the present invention.
Conventional and well-known processes for making the orifice plate and charge plate separately consist of photolithography and nickel electroforming. Orifice plate fabrication methods are disclosed in U.S. Pat. Nos. 4,374,707; 4,678,680; and 4,184,925. Orifice plate fabrication generally involves the deposition of a nonconductive thin disk followed by partial coverage of this with nickel to form an orifice. After formation of the orifice, the metal substrate is selectively etched away leaving the orifice plate electroform as a single component. Charge plate electroforming is described in U.S. Pat. Nos. 4,560,991 and 5,512,117. These charge plates are made by depositing nonconductive traces on a metal substrate followed by deposition of nickel in a similar fashion to orifice plate fabrication, except that parallel lines of metal are formed instead of orifices. Nickel, which is a ferromagnetic material, is unsuitable for use with magnetic inks. Nor can low pH ink (pH less than, say, 6) be used with nickel, which is etched by low pH ink.
Epoxy is generally used to bond the separately fabricated charge plate and orifice plate. Using epoxy in bonding is often called “adhesive bonding” and limits yield. Nor does epoxy bonding provide a very robust connection. It is very easy to introduce the trapped air between the two components, so it is normally not a void-free bonding technique. The anodic bonding is a relatively low temperature process (the temperature can be as low as 350° C.), but with a higher bonding strength, and is normally a void-free bonding.
Accordingly, it is an object of the present invention to provide a fabrication process of the orifice plate and charge plate that permits the use of both low pH and magnetic inks. It is another object of the present invention to provide such an orifice plate and charge plate as one, self-aligned component with high yield and robust connection.